The trials fields, at the back of Battleston Hill at RHS Wisley in Surrey, are easy to miss. You have to turn your back on the temptations of double herbaceous borders, rose gardens and the rest and walk over a socking great big hill to put yourself through a battering from thundering traffic noise from the A3 just the other side of the hedge. But it’s actually the most important bit of the whole garden.

That’s because this is the principal place where the RHS does its trials (they also run trials at other locations, like Brogdale in Kent and other RHS gardens just to see how plants perform in different climatic conditions).

Long beds are planted with dozens of different varieties of one particular genus: on the day I visited the trials included hibiscus, rosemary, petunias, beetroot and strawberries (and those are only the ones I can remember).

It is rare that you get to see multiple varieties of the same type of plant alongside each other, so you can compare and contrast, and perhaps decide which ones you might like in your own garden. Even better, if you wait till the trials report (they’re published on the RHS website at the end of each trial) you’ll find out how your chosen varieties perform, too. If they get an AGM you know you’re on to a winner.

One of the most eyecatching displays this year is the bed of Cosmos, in full spectacular flower on my visit and looking just glorious. It is – who knew? – the Year of the Cosmos, according to ornamental plant industry people Fleuroselect anyway. It’s as good an excuse as any to explore what this surprisingly diverse group of plants can do – and to get a sneak peek of the new varieties coming soon to a seed merchant’s near you. Here are a few which caught my eye:

‘Casanova Red’ 3ft tall and delightful with three tones of flower on one plant

C. sulphureus ‘Cosmic Red’ I had no idea cosmos come in orange, too. C. sulphureus produces smaller flowers (about 2″ across) than the more familiar C. bipinnatus but there are loads of them.

‘Cosimo Red-White’ Quite short, at 2 1/2 ft, and very dainty with small, almost wild-looking flowers over sparse foliage: wouldn’t look out of place in an annual meadow

‘Xanthos’ This is, I believe, already on the market and I’ll be buying it next year: lovely palest lemon flowers opening deeper primrose

‘Carioca’ Beautiful clear orange over lush foliage, about 3ft tall

‘Double Click Rose Bonbon’ Already a favourite of mine, only confirmed by seeing it en masse alongside other cosmos. I like the variability of the flowers, with some fully double, others semi-double and others (like this one) hardly double at all

‘Cupcakes White’ A new shape of cosmos flower on the way with petals fused to make a large bowl-shaped bloom on a tall (5ft) plant. Not sure whether it’ll catch on: it loses some of the daintiness of a regular cosmos.

‘Pied Piper Red’ And another curiosity: this time quilled petals. I like the two-tone effect from the inner and outer petals, but it’s not as elegant as a single.

C. sulphureus ‘Tango’ Retina-searing shade of orange with quite small flowers but loads of them. Medium-sized plant, to about 4ft.